T-cell energy metabolism as a controller of cell fate in transplantation. Curr Opin Organ Transplant. 2015;20:21-28. [PMID: 25563988 DOI: 10.1097/mot.0000000000000149]

Glycolysis Changes in Alloreactive Memory B Cells in Highly Sensitized Kidney Transplant Recipients Undergonig Desensitization Therapy

Despite the growing use of desensitization strategies, hyperimmune patients remain at high risk of antibody-mediated rejection suggesting that, even when donor-specific antibodies (DSA) are effectively depleted, anti-donor specific B cells persist. We included 10 highly sensitized recipients that underwent desensitization with plasmapheresis and B cell depletion prior to kidney transplantation. We quantified changes in DSA (luminex), total B-cell subsets (flow cytometry), anti-donor HLA B cells (fluorospot), and single-cell metabolism in serially collected samples before desensitization, at the time of transplant, and at 6 and 12 months thereafter. Desensitization was associated with a decrease in DSA and total memory B cell and naive B cell percentage, while plasma cells and memory anti-donor HLA circulating B cells persisted up to 12 months after transplant. At 12-month post-transplantation, memory B cells increased their glycolytic capacity, while proliferative KI67+ plasma cells modified their metabolism by increasing fatty acid and amino acid oxidation capacity and decreasing their glucose dependence. Despite effective DSA depletion, anti-donor B cells persist in kidney transplant recipients. Due to the reliance of these cells on glycolysis, glycolysis-targeting therapies might represent a valuable treatment strategy.

Harnessing Immune Cell Metabolism to Modulate Alloresponse in Transplantation

Immune cell metabolism plays a pivotal role in shaping and modulating immune responses. The metabolic state of immune cells influences their development, activation, differentiation, and overall function, impacting both innate and adaptive immunity. While glycolysis is crucial for activation and effector function of CD8 T cells, regulatory T cells mainly use oxidative phosphorylation and fatty acid oxidation, highlighting how different metabolic programs shape immune cells. Modification of cell metabolism may provide new therapeutic approaches to prevent rejection and avoid immunosuppressive toxicities. In particular, the distinct metabolic patterns of effector and suppressive cell subsets offer promising opportunities to target metabolic pathways that influence immune responses and graft outcomes. Herein, we review the main metabolic pathways used by immune cells, the techniques available to assay immune metabolism, and evidence supporting the possibility of shifting the immune response towards a tolerogenic profile by modifying energetic metabolism.

Review of prognostic factors for kidney transplant survival

Transplantation is the most effective treatment for end-stage chronic kidney disease, as this procedure prolongs and improves the patient's quality of life. One of the key problems is the risk of graft rejection. The purpose of this research was to identify and analyse prognostic factors that will prevent rejection. In particular, the prognostic factors grouped by methods of synthesis, generalisation and statistical processing with calculation and graphical representation of hazard ratio and correlation coefficient were grouped, namely: age of donor and recipient, time of cold kidney ischaemia, duration of preoperative dialysis, body mass index, presence of concomitant diseases (diabetes mellitus, hypertension), primary causes causing transplantation. Several molecular genetic and biochemical prognostic markers (transcription factors, immunocompetent cell signalling and receptors, cytostatin C, creatinine, citrate, lactate, etc.) are annotated. It has been demonstrated that creatinine reduction rate determines the risk of rejection, displaying the dynamics of cystatin C and creatinine changes in the postoperative period. Young recipients who underwent prolonged preoperative dialysis were identified as having the highest risk of rejection. Diabetes and hypertension bear a non-critical but commensurately equal risk of rejection. The survival rate of the graft is better when transplanted from a living donor than from a deceased donor. A correlation between cold ischaemia time, body mass index and the probability of graft failure has been proven, namely, the greater the donor and recipient body mass index and the longer the cold ischaemia time, the lower the chance of successful long-term organ acclimation. The data obtained can be used as prognostic factors for graft accommodation at different intervals after surgery.

Tumorous expression of NAC1 restrains antitumor immunity through the LDHA-mediated immune evasion

BACKGROUND

T cell-mediated antitumor immunity has a vital role in cancer prevention and treatment; however, the immune-suppressive tumor microenvironment (TME) constitutes a significant contributor to immune evasion that weakens antitumor immunity. Here, we explore the relationship between nucleus accumbens-associated protein-1 (NAC1), a nuclear factor of the BTB (broad-complex, Tramtrack, bric a brac)/POZ (Poxvirus, and Zinc finger) gene family, and the TME.

METHODS

Adoptive cell transfer (ACT) of mouse or human tumor antigen (Ag)-specific CD8+ cytotoxic T lymphocytes (CTLs) was tested in an immunocompetent or immunodeficient mouse model of melanoma with or without expression of NAC1. The effects of NAC1 expression on immune evasion in tumor cells were assessed in vitro and in vivo. CRISPR/Cas9, glycolysis analysis, retroviral transduction, quantitative real-time PCR, flow cytometric analysis, immunoblotting, database analyses were used to screen the downstream target and underlying mechanism of NAC1 in tumor cells.

RESULTS

Tumorous expression of NAC1 negatively impacts the CTL-mediated antitumor immunity via lactate dehydrogenase A (LDHA)-mediated suppressive TME. NAC1 positively regulated the expression of LDHA at the transcriptional level, which led to higher accumulation of lactic acid in the TME. This inhibited the cytokine production and induced exhaustion and apoptosis of CTLs, impairing their cell-killing ability. In the immunocompetent and immunodeficient mice, NAC1 depleted melanoma tumors grew significantly slower and had an elevated infiltration of tumor Ag-specific CTLs following ACT, compared with the control groups.

CONCLUSIONS

Tumor expression of NAC1 contributes substantially to immune evasion through its regulatory role in LDHA expression and lactic acid production. Thus, therapeutic targeting of NAC1 warrants further exploration as a potential strategy to reinforce cancer immunotherapy, such as the ACT of CTLs.

Proteomics Analysis of Aqueous Humor and Rejected Graft in Pig-to-Non-Human Primate Corneal Xenotransplantation

Although pig-to-non-human primate (NHP) corneal xenotransplantation has shown long-term graft survival, xenogeneic antigen-related immune responses are still stronger than allogeneic antigen-associated responses. Therefore, there is an unmet need to investigate major rejection pathways in corneal xenotransplantation, even with immunosuppression. This study aimed to identify biomarkers in aqueous humor for predicting rejection and to investigate rejection-related pathways in grafts from NHPs transplanted with porcine corneas following the administration of steroids combined with tacrolimus/rituximab. NHPs who had received corneas from wild-type (WT) or α-1,3-galactosyltransferase gene-knockout (GTKO) pigs were divided into groups with or without rejection according to clinical examinations. Liquid chromatography-mass spectrometry (LC-MS) was used to analyze the proteomes of corneal tissues or aqueous humor. The biological functions of differentially expressed proteins (DEPs) were assessed using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) for pathways and protein–protein interaction network analysis. Among the 66 DEPs in aqueous humor, complement proteins (C3, C5, and C9) and cholesterol metabolic proteins (APOA1 and APOA2) were related to xenogeneic rejection as biomarkers, and alternative pathways of the complement system seemed to be important in xenogeneic graft rejection. Among the 416 DEPs of the cornea, NF-κB1 and proteosomes (PSMD7, PSMA5, and PSMD3) seemed to be related to xenogeneic graft rejection. Additionally, oxidative phosphorylation and leukocyte activation-related pathways are involved in rejection. Overall, our proteomic approach highlights the important role of NF-κB1, proteosomes, oxidative phosphorylation, and leukocyte activation-related inflammation in the cornea and the relevance of complement pathways of the aqueous humor as a predictive biomarker of xenogeneic rejection.

Tumor-Induced Metabolism and T Cells Located in Tumor Environment

Several subtypes of T cells are located in a tumor environment, each of which supplies their energy using different metabolic mechanisms. Since the cancer cells require high levels of glucose, the conditions of food poverty in the tumor environment can cause inactivation of immune cells, especially the T-effector cells, due to the need for glucose in the early stages of these cells activity. Different signaling pathways, such as PI3K-AKt-mTOR, MAPK, HIF-1α, etc., are activated or inactivated by the amount and type of energy source or oxygen levels that determine the fate of T cells in a cancerous environment. This review describes the metabolites in the tumor environment and their effects on the function of T cells. It also explains the signaling pathway of T cells in the tumor and normal conditions, due to the level of access to available metabolites and subtypes of T cells in the tumor environment.

STAT3 Activation-Induced Fatty Acid Oxidation in CD8+ T Effector Cells Is Critical for Obesity-Promoted Breast Tumor Growth

Although obesity is known to be critical for cancer development, how obesity negatively impacts antitumor immune responses remains largely unknown. Here, we show that increased fatty acid oxidation (FAO) driven by activated STAT3 in CD8+ T effector cells is critical for obesity-associated breast tumor progression. Ablating T cell Stat3 or treatment with an FAO inhibitor in obese mice spontaneously developing breast tumor reduces FAO, increases glycolysis and CD8+ T effector cell functions, leading to inhibition of breast tumor development. Moreover, PD-1 ligation in CD8+ T cells activates STAT3 to increase FAO, inhibiting CD8+ T effector cell glycolysis and functions. Finally, leptin enriched in mammary adipocytes and fat tissues downregulates CD8+ T cell effector functions through activating STAT3-FAO and inhibiting glycolysis. We identify a critical role of increased oxidation of fatty acids driven by leptin and PD-1 through STAT3 in inhibiting CD8+ T effector cell glycolysis and in promoting obesity-associated breast tumorigenesis.

Peripheral blood transcriptome analysis and development of classification model for diagnosing antibody-mediated rejection vs accommodation in ABO-incompatible kidney transplant

The major obstacle to successful ABO blood group-incompatible kidney transplantation (ABOi KT) is antibody-mediated rejection (AMR). This study aimed to investigate transcriptional profiles through RNA sequencing and develop a minimally invasive diagnostic tool for discrimination between accommodation and early acute AMR in ABOi KT. Twenty-eight ABOi KT patients were selected: 18 with accommodation and 10 with acute AMR at the 10th day posttransplant protocol biopsy. Complete transcriptomes of their peripheral blood were analyzed by RNA sequencing. Candidate genes were selected by bioinformatics analysis, validated with quantitative polymerase chain reaction, and used to develop a classification model to diagnose accommodation. A total of 1385 genes were differentially expressed in accommodation compared with in AMR with P-adjusted < .05. Functional annotation and gene set enrichment analysis identified several immune-related and immunometabolic pathways. A 5-gene classification model including COX7A2L, CD69, CD14, CFD, and FOXJ3 was developed by logistic regression analysis. The model was further validated with an independent cohort and discriminated between accommodation and AMR with 92.7% sensitivity, 85.7% specificity, and 91.7% accuracy. Our study suggests that a classification model based on peripheral blood transcriptomics may allow minimally invasive diagnosis of acute AMR vs accommodation and subsequent patient-tailored immunosuppression in ABOi KT.

Detection of lung transplant rejection in a rat model using hyperpolarized [1-13 C] pyruvate-based metabolic imaging

The current standard for noninvasive imaging of acute rejection consists of X-ray/CT, which derive their contrast from changes in ventilation, inflammation and edema, as well as remodeling during rejection. We propose the use of hyperpolarized [1-¹³ C] pyruvate MRI-which provides real-time metabolic assessment of tissue-as an early biomarker for tissue rejection. In this preliminary study, we used μCT-derived parameters and HP ¹³ C MR-derived biomarkers to predict rejection in an orthotopic left lung transplant model in both allogeneic and syngeneic rats. On day 3, the normalized lung density-a parameter that accounts for both lung volume (mL) and density (HU)-was -0.335 (CI: -0.598, -0.073) and - 0.473 (CI: -0.726, -0.220) for the allograft and isograft, respectively (not significant, 0.40). The lactate-to-pyruvate ratios-derived from the HP ¹³ C MRI-for the allograft and isograft were 0.200 (CI: 0.161, 0.240) and 0.114 (CI: 0.074, 0.153), respectively (significant, 0.020). Both techniques showed tissue rejection on day 7. A separate sub-study revealed CD8+ cells as the primary source of the lactate-to-pyruvate signal. Our study suggests that hyperpolarized (HP) [1-¹³ C] pyruvate MRI is a promising early biomarker for tissue rejection that provides metabolic assessment in real time based on changes in cellularity and metabolism of lung tissue and the infiltrating inflammatory cells, and may be able to predict tissue rejection earlier than X-ray/CT.

Immunometabolism: A target for the comprehension of immune response toward transplantation

Organ transplantation is a life-saving procedure, however predicting graft survival is still challenging. Understanding immune-cell pathobiology is critical to the development of effective therapies to prevent rejection. Over the recent years it has become progressively evident that the complex nature of immune cell behavioral dynamics is strongly dependent on cellular metabolism, which in turn, relies on competition for nutrients, oxygen and metabolites with other immune cells and microbiota. Furthermore, the influence of the inflammatory state can lead to substantial changes in conditions within the tissue micro-environment. Considering the context of immunity, alterations in metabolic pathways (glycolysis, the tricarboxylic acid cycle, the pentose phosphate pathway, the fatty acid oxidation and synthesis, and the amino acid metabolic pathways) will influence the production of different sets of cytokines and affect transplantation outcome. It is now known that naïve, resting and effector cells acquire different metabolic profiles and studies have shown that specifically targeting some of these metabolic routes can prevent differentiation of effector T cells in favor of Tregs. Ultimately, to develop effective therapies that will prevent graft loss and understanding how cell metabolism impacts the fate and function of immune cells is now a critical point of discussion. The distinct metabolic features and requirements observed in effector and suppressive cell subsets offer promising opportunities for selective regulation of the immune responses in transplantation and will be discussed in this review.

Inflammation research sails through the sea of immunology to reach immunometabolism

Inflammation occurs as a result of acute trauma, invasion of the host by different pathogens, pathogen-associated molecular patterns (PAMPs) or chronic cellular stress generating damage-associated molecular patterns (DAMPs). Thus inflammation may occur under both sterile inflammatory conditions including certain cancers, autoimmune or autoinflammatory diseases (Rheumatic arthritis (RA)) and infectious diseases including sepsis, pneumonia-associated acute lung inflammation (ALI) or acute respiratory distress syndrome (ARDS). The pathogenesis of inflammation involves dysregulation of an otherwise protective immune response comprising of various innate and adaptive immune cells and humoral (cytokines and chemokines) mediators secreted by these immune cells upon the activation of signaling mechanisms regulated by the activation of different pattern recognition receptors (PRRs). However, the pro-inflammatory and anti-inflammatory action of these immune cells is determined by the metabolic stage of the immune cells. The metabolic process of immune cells is called immunometabolism and its shift determined by inflammatory stimuli is called immunometabolic reprogramming. The article focuses on the involvement of various immune cells generating the inflammation, their interaction, immunometabolic reprogramming, and the therapeutic targeting of the immunometabolism to manage inflammation.

Role of miR-449a in the Activation and Metabolism of CD4+ T Cells

BACKGROUND

Acute rejection is a significant challenge after organ transplantation. The CD4⁺ T-cell‒mediated immune response plays an important role in acute transplant rejection. It was also found that miR-449a microRNA regulates the alloimmune response in a model of heart transplantation in mice. Our goal was to determine the role of miR-449a in the regulation of CD4⁺ T cells.

METHODS

We examined miR-449a expression in peripheral blood mononuclear cells (PBMCs) and graft-infiltrating lymphocytes (GILs) between syngeneic transplant and allogeneic transplant groups on day 7 post‒heart transplantation. We also examined miR-449a expression in CD4⁺ T-cell activation and mixed-lymphocyte reactions (MLRs) in vitro. To evaluate the effect of miR-449a on CD4⁺ T-cell metabolism, we analyzed key metabolic parameters using XFp extracellular flux analyses.

RESULTS

Our in vivo heart transplant models showed that the expression of miR-449a in PBMCs and in GILs significantly increased in the allogeneic groups in comparison to the syngeneic groups (P < .01). Furthermore, in vitro analysis confirmed that the expression of miR-449a was significantly elevated in activated CD4⁺ T cells. Reduction of miR-449a expression in CD4⁺ T cells decreased the mitochondrial respiration in the same CD4⁺ T cells.

CONCLUSION

Our results reveal that miR-449a microRNA was elevated in allogeneic heart allografts. This correlated with an increased miR-449a expression in activated CD4⁺ T cells. Inhibition of miR-449a in activated CD4⁺ T cells coincided with reduced mitochondrial respiration, suggesting that miR-449a influences CD4⁺ T-cell activation during the alloimmune response by regulating metabolic status.

Immunometabolism and PI(3)K Signaling As a Link between IL-2, Foxp3 Expression, and Suppressor Function in Regulatory T Cells

CD4⁺ Foxp3⁺ regulatory T cells (Tregs) are an essential component of immune homeostasis. Modulation of Treg function has been proposed as a means of treating autoimmune conditions and preventing rejection of organ transplants, although achieving this goal will require a detailed understanding of Treg signaling pathways. Signaling within Tregs is known to differ considerably from that observed in other T cell subsets. Of note, Tregs are the only cell type known to constitutively express CD25, the main ligand-binding subunit of the IL-2 receptor. The PI(3)K/Akt/mTOR cascade constitutes a major signaling pathway downstream of IL-2 and is closely tied to cellular metabolism. Due to increasing recognition of the links between cellular fuel usage and immune cell function, the interplay between IL-2 signaling and Treg metabolism represents an important space for exploration and a potential approach for immunomodulation. Here, we discuss how IL-2 may affect Treg metabolism via PI(3)K signaling, as well as the effects of altered metabolism on Treg lineage stability and suppressor function.

JAK/STAT3-Regulated Fatty Acid β-Oxidation Is Critical for Breast Cancer Stem Cell Self-Renewal and Chemoresistance

Cancer stem cells (CSCs) are critical for cancer progression and chemoresistance. How lipid metabolism regulates CSCs and chemoresistance remains elusive. Here, we demonstrate that JAK/STAT3 regulates lipid metabolism, which promotes breast CSCs (BCSCs) and cancer chemoresistance. Inhibiting JAK/STAT3 blocks BCSC self-renewal and expression of diverse lipid metabolic genes, including carnitine palmitoyltransferase 1B (CPT1B), which encodes the critical enzyme for fatty acid β-oxidation (FAO). Moreover, mammary-adipocyte-derived leptin upregulates STAT3-induced CPT1B expression and FAO activity in BCSCs. Human breast-cancer-derived data suggest that the STAT3-CPT1B-FAO pathway promotes cancer cell stemness and chemoresistance. Blocking FAO and/or leptin re-sensitizes them to chemotherapy and inhibits BCSCs in mouse breast tumors in vivo. We identify a critical pathway for BCSC maintenance and breast cancer chemoresistance.

Targeting Metabolism as a Novel Therapeutic Approach to Autoimmunity, Inflammation, and Transplantation

Immune cell activation and differentiation occurs concurrently with metabolic reprogramming. This ensures that activated cells generate the energy and substrates necessary to perform their specified function. Likewise, the metabolic programs among different cells of the immune system vary. By targeting different metabolic pathways, these differences allow for selective regulation of immune responses. Further, the relative susceptibility of cells to a metabolic inhibitor is dictated by their metabolic demands; cellular selectivity is based on demand. Therefore, where differences exist in metabolic pathways between healthy and pathogenic cells, there is opportunity for selective regulation with agents lacking intrinsic specificity. There are now a host of studies demonstrating how inhibitors of metabolism (e.g., glycolysis, glutamine metabolism, and fatty acid oxidation) can regulate immune responses and treat immune-mediated pathogenesis. In this brief review we detail how inhibitors of metabolism can be employed to regulate immune responses in both autoimmunity and transplantation.

Immunometabolism of regulatory T cells

The bidirectional interaction between the immune system and whole-body metabolism has been well recognized for many years. Via effects on adipocytes and hepatocytes, immune cells can modulate whole-body metabolism (in metabolic syndromes such as type 2 diabetes and obesity) and, reciprocally, host nutrition and commensal-microbiota-derived metabolites modulate immunological homeostasis. Studies demonstrating the metabolic similarities of proliferating immune cells and cancer cells have helped give birth to the new field of immunometabolism, which focuses on how the cell-intrinsic metabolic properties of lymphocytes and macrophages can themselves dictate the fate and function of the cells and eventually shape an immune response. We focus on this aspect here, particularly as it relates to regulatory T cells.

Role of Memory T Cells in Allograft Rejection and Tolerance

Memory T cells are characterized by their low activation threshold, robust effector functions, and resistance to conventional immunosuppression and costimulation blockade. Unlike their naïve counterparts, memory T cells reside in and recirculate through peripheral non-lymphoid tissues. Alloreactive memory T cells are subdivided into different categories based on their origins, phenotypes, and functions. Recipients whose immune systems have been directly exposed to allogeneic major histocompatibility complex (MHC) molecules display high affinity alloreactive memory T cells. In the absence of any prior exposure to allogeneic MHC molecules, endogenous alloreactive memory T cells are regularly generated through microbial infections (heterologous immunity). Regardless of their origin, alloreactive memory T cells represent an essential element of the allograft rejection process and a major barrier to tolerance induction in clinical transplantation. This article describes the different subsets of alloreactive memory T cells involved in transplant rejection and examine their generation, functional properties, and mechanisms of action. In addition, we discuss strategies developed to target deleterious allospecific memory T cells in experimental animal models and clinical settings.

Selective Sparing of Human Tregs by Pharmacologic Inhibitors of the Phosphatidylinositol 3-Kinase and MEK Pathways

Phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase/extracellular signal-regulated (MEK) signaling are central to the survival and proliferation of many cell types. Multiple lines of investigation in murine models have shown that control of the PI3K pathway is particularly important for regulatory T cell (Treg) stability and function. PI3K and MEK inhibitors are being introduced into the clinic, and we hypothesized that pharmacologic inhibition of PI3K, and possibly MEK, in mixed cultures of human mononuclear cells would preferentially affect CD4(+) and CD8(+) lymphocytes compared with Tregs. We tested this hypothesis using four readouts: proliferation, activation, functional suppression, and signaling. Results showed that Tregs were less susceptible to inhibition by both δ and α isoform-specific PI3K inhibitors and by an MEK inhibitor compared with their conventional CD4(+) and CD8(+) counterparts. These studies suggest less functional reliance on PI3K and MEK signaling in Tregs compared with conventional CD4(+) and CD8(+) lymphocytes. Therefore, the PI3K and MEK pathways are attractive pharmacologic targets for transplantation and treatment of autoimmunity.

Distinctive Expression of Bcl-2 Factors in Regulatory T Cells Determines a Pharmacological Target to Induce Immunological Tolerance

Distinctive molecular characteristics of functionally diverse lymphocyte populations may represent novel pharmacological targets for immunotherapy. The intrinsic apoptosis pathway is differently regulated among conventional and regulatory T cells (Tregs). Targeted pharmacological modulation of this pathway with a small molecule Bcl-2/Bcl-xL inhibitor (ABT-737) caused a selective depletion of effector T cells and a relative enrichment of Tregs in vivo. Treatment with ABT-737 resulted in a tolerogenic milieu, which was exploited to alleviate graft-versus-host disease, to prevent allograft rejection in a stringent fully MHC-mismatched skin transplantation model and to induce immunological tolerance in combination with bone marrow transplantation. This concept has the potential to find various applications for immunotherapy, since it allows pharmacologic exploitation of the immunomodulatory properties of Tregs without the need for cell manipulation ex vivo.